Calculate cell potential at non-standard conditions, or solve for any variable in the Nernst equation.
Enter the standard cell potential (E°), number of electrons transferred (n), reaction quotient (Q), and temperature. The calculator finds the cell potential (E) at those non-standard conditions. You can also solve for E° or Q by selecting the appropriate button.
For half-cell calculations, use the standard reduction potential for E° and the concentration ratio for Q. For full cell calculations, E° is the difference between cathode and anode standard potentials.
The Nernst equation relates the cell potential to the standard potential and the concentrations of reactants and products: E = E° − (RT/nF) × ln(Q), where R is the gas constant (8.314 J/(mol·K)), T is temperature in Kelvin, n is electrons transferred, F is Faraday's constant (96,485 C/mol), and Q is the reaction quotient.
Worked example: A Daniell cell (Zn/Cu) has E° = 1.10 V with n = 2. If [Zn²⁺] = 1.0 M and [Cu²⁺] = 0.01 M, then Q = [Zn²⁺]/[Cu²⁺] = 100. At 25°C: E = 1.10 − (0.02569/2) × ln(100) = 1.10 − 0.0591 = 1.041 V.
At equilibrium, E = 0 and Q = K (the equilibrium constant). This gives the relationship ln(K) = nFE°/RT, which connects thermodynamics to electrochemistry.
ΔG and E: The Gibbs free energy change is related to cell potential by ΔG = −nFE. A positive E means spontaneous (ΔG < 0), while a negative E means non-spontaneous.